Optical Transmitter for Computing Applications

ABSTRACT

A compact optical transceiver is provided in which a substrate provides for an alignment surface for optical fibers and a lens assembly provides the necessary optical paths for coupling to photodiode and photodetector structures. Appropriate electrical connections on the substrate enable the substrate to be directly connected to a printed circuit board, grid array socket, and the like.

BACKGROUND OF THE INVENTION

With the continuing growth in performance of computing technology, theinterconnect bandwidth required among microprocessors, memories, andinput/output devices continues to increase. Such high speeds createincreasing problems for the technology used for interconnections amongthe microprocessors, memories, and input/output devices. For example,copper trace technology, such as conventionally employed on printedcircuit boards, is expected to be limited to 15-20 Gigabits per secondas a result of signal degradation, power dissipation, andelectromagnetic interference unavoidable at such high clock speeds.

Manufacturers of many electronic products have sought to address thelimitations of copper by using more exotic substrates with lowerdielectric loss or using more sophisticated input/output equalizers atthe transmitter and receiver. Unfortunately all of these potentialsolutions are costly and power consumptive. Therefore traditionalinterconnect scaling will no longer satisfy performance requirements.Defining and finding solutions beyond copper and low dielectric lossmaterial will require innovation in design, packaging and unconventionalinterconnect technology.

One alternative attracting increasing attention is the use of opticalinterconnect technology. Optical communication technology has been usedfor many years in long distance applications such as telephony and theinternet, and is now sometimes implemented for use in shorter distanceapplications for the enterprise such as storage area networks andrack-to-rack interconnections. Such optical technology has alreadydemonstrated that at high frequencies, the optical fibers provide longerdistance-higher bandwidth capability as compared with electrical cables,yet minimize loss in the transmitted signal.

Unfortunately, optical interconnect technology has associated with it aseparate set of implementation difficulties. These difficulties includeoptical coupling efficiencies, fiber alignment, complex packagingtechnologies, including hermeticity, thermal management, electricalperformance, and manufacturability—the ease of assembly and amenabilityto automation. Thus, generally speaking, current optical modules ortransceivers like SFP, 300 pins MSA, Xenpack, Xpak, X2 and XFP formfactors provided by various suppliers including Emcore, Finisar,Agilent, and Bookham are still complex to manufacture and expensive.

Additionally for substantial utility in the computing market, opticaltransceivers also need (1) extremely low power consumption to competewith electrical solutions, (2) a smaller form factor adapted for andappropriate to the computer industry, and (3) very large interconnectbandwidth to provide data consummate with processing power. One exampleof a prior art solution is the IBM Terabus project (Exploitation ofoptical interconnects in future server architectures, Benner et al., 49IBM J. Res. & Dev. No. 4/5, July/September 2005). In this concept thetransmitter and receiver modules are separate and require a complexstructure with multiple chips/modules mounted on a substrate—one modulewith an array of transmitters and another module with an array ofreceivers.

A novel solution adapted for computing application to interconnectprocessing units while increasing communication bandwidth, maintainingan ultra small form factor, decreasing power consumption, simplifyingand enabling automated assembly is required.

BRIEF SUMMARY OF THE INVENTION

This invention provides an electro-optical transceiver which includes asubstrate having a generally planar configuration to which all of thecomponents of the transceiver are mounted. The substrate includes acavity on the lower surface. Electrical contacts for connections toexternal circuitry around the cavity are provided on a lower surface ofthe substrate, and, in one embodiment, a further set of electricalcontacts is disposed on the upper surface of the substrate for beingconnected to an integrated circuit. The integrated circuit is affixed tothe upper surface of the substrate and connected to the second set ofcontacts. A multi-port lens assembly is also affixed to the substrate toreceive light from optical fibers, and transmit light to optical fiberscoupled to the substrate. Each of the light-sensing and light-emittingdevices is electrically connected to the integrated circuit. The generalorientation of the transceiver enables electrical contacts to be made inone direction and heat to dissipate in the opposite direction, withconnections to optical fibers being made perpendicularly to thedirection of heat dissipation.

In a further embodiment of the invention, the integrated circuit ismounted into the substrate cavity under the lens assembly. Aheat-spreading device affixed to the substrate dissipates heat from theintegrated circuit.

Embodiments of the present invention advantageously decrease thecomplexity of the manufacturing and reduce the size of the transceiver.By eliminating the transceiver enclosure and using the substrate as amulti-function core element, we reduce the number of components of thetransceiver. The substrate acts here as a skeleton. Through eliminationof optical pluggability, the transceiver size and form factor arefavorably reduced. Furthermore associated with low cost manufacturingtechnology capable of mass-production, e.g. molding, lamination, waferprocessing, and automated pick and place, the transceiver cost isminimized.

In another embodiments of this invention a new alignment technology forthe optical components is provided. Enabled by the short communicationdistance between computing nodes (below 100 meters), the use ofmulti-mode fibers alleviate the packaging and alignment cost of thetransceiver compared to the long distance single-mode fiber applications(greater than 300 m). Precise alignment guiding structure is provided toaccurately reference the EO converters to the substrate, the substrateto the optical element and finally the optical element to the opticalfibers.

A further embodiment of this novel transceiver utilizes multiplechannels (parallel optics). By implementing multi-channels to thetransceiver, the cost per unit bandwidth is spread across the packagingcost. Preferably all the different channels share common components, forexample, the same substrate, the same optical element, the same analogintegrated circuit and the same bundle of fibers.

Other features and advantages of the invention will be apparent in viewof the following detailed description and preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an optical transceiver;

FIG. 2 is a bottom view of the optical transceiver of FIG. 1;

FIG. 3 illustrates a device for electrically connecting the opticaltransceiver;

FIG. 4 illustrates a device for electrically connecting the opticaltransceiver;

FIG. 5 is an exploded view of one embodiment of the optical transceiver;

FIG. 6 is an exploded view of alignment guide pins and holes used toposition the multi-port lens;

FIG. 7 is an exploded view of an alternate construction for the opticaltransceiver;

FIG. 8 is a cross sectional view showing an interior portion of theoptical transceiver;

FIG. 9 is a cross sectional view showing an alternative opticaltransceiver;

FIG. 10 is a perspective view illustrating the light path within theoptical transceiver;

FIG. 11 illustrates a server motherboard with an optical host adaptercard;

FIG. 12 illustrates a server motherboard with an integrated opticaltransceiver; and

FIG. 13 illustrates a server motherboard with an optical DIMM extensionfor the transceiver.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a top view of an optical transceiver according to a preferredembodiment of this invention. The transceiver is depicted on a U.S.quarter dollar coin 5 to illustrate the compact size of the transceiver.The transceiver functions to convert optical signals arriving on opticalfibers 10 to electrical signals, and provides them as an output fromelectrical contacts on the lower surface of the transceiver (not shownin FIG. 1, but see FIG. 2). In addition electrical signals provided tothe contacts are converted to optical signals and provided on theoptical fibers 10. The device preferably operates as a parallelmultimode transceiver with multiple ports, preferably six outputs andsix inputs. Of course, different numbers of inputs and outputs, eitherbalanced or unbalanced, can be used. The module 12 illustrated in FIG. 1includes appropriate electrical terminals, enabling it to be directlymounted on a printed circuit board (PCB), for example, using compliantcontacts to ensure electrical connections as shown in more detail inFIG. 2.

FIG. 2 illustrates the optical transceiver viewed from the lower surfaceto which electrical connections are provided via electrical contacts 19.The optical fibers 10 are shown as mounted to the multi-port lens 24.The multi-port lens assembly is preferably made from Ultem (transparentorganic material) and manufactured by precise injection molding, atypical approach for manufacturing in high volumes. The fibers arepositioned in the appropriate locations to align them with optical pathsto the multi-port lens 24 by a corresponding series of grooves 18. Themulti-port lens is mounted onto the substrate 15 and is preciselyaligned to it by guiding pins (See FIG. 6). In this manner the opticalfibers, the multi-port lens and the optoelectronic devices can bealigned appropriately, as will be described in more detail below.

Light is provided to the fibers by a series of light-emitting diodes,preferably vertical cavity surface emitting laser (VCSEL) diodes,mounted in the substrate cavity, and light is received from the fibersby a series of light sensing elements, preferably p-i-n (or PIN). Suchphotodiodes provide an intrinsic (undoped) region between the n- andp-doped regions. PINs or other suitable photo-detecting devices, arepositioned in the same substrate cavity. The emitting diodes and thephoto-detecting devices are precisely positioned relative to thesubstrate guiding pins (See FIG. 6). The light is reflected through a90° angle by internal reflection interface which is part of cavities 22shown in FIG. 2. The lenses 24, internal reflection cavities 22,photodetectors, and laser diodes will all be described in more detailbelow. In one implementation the VCSEL array and the PIN array arestaggered to minimize the width of the transceiver and minimize opticaland electrical interference between transmitters and receivers.

In the depicted implementation, compliant contacts 19 are providedacross the lower surface of the substrate 15. In one embodiment, thecontacts are provided by resilient metal “fingers” positioned overrecessed areas in the substrate. In this manner, bumps on the fingers oron the board to which the transceiver is connected, are mechanicallypressed against the compliant fingers to assure reliable electricalconnections.

In the preferred implementation (See FIG. 3) a compliant contact socket25 is used to provide electrical contact from the transceiver 12 to theunderlying printed circuit board (PCB). The contact is created throughrubber bumps 20 filled with metallic particles between the metallic padsof the PCB and the metallic pads on the lower surface of the substrate.This socket 27 is sandwiched between the device and the PCB. The bumpsare compressed by a loading force applied on the top of the transceiver12. Such socket technology is available from Tyco Electronics and isreferred to by Tyco as the HXC-LGA system. In this technology,conductive particles are molded into an insulating material formed in acolumnar shape. When the insulating material is compressed, the metalparticles with in the column link together and provide an electricalinterconnection through the column.

Another approach to providing electrical connections between thetransceiver and the underlying PCB is shown in FIG. 4. As shown there, aLand Grid Array socket 27 (commercially available) has positioningcompliant fingers 28. Those fingers hold the optical transceiver tightlyto the socket and enable a precise alignment of the socket electricalpins 30 to the corresponding substrate lower contact pads. Theelectrical pins in the socket are preferably compliant enabling them tobe pressed tightly against the conductive regions. The socket issoldered to the PCB. Similarly to the previous approach, the socket issandwiched between the device and the PCB. The socket pins 30 arecompressed by a loading force applied on the top of the transceiver.Because the pads are on the underside of substrate 15 they are notvisible in FIG. 3.

FIG. 5 illustrates the structure of the optical transceiver in furtherdetail. As shown, a multilayered substrate 15 is employed. Each layer inthe substrate preferably comprises material compatible with the otherlayers. Conventional ceramic or organic material systems are used. Layer15 a includes contact regions 33 for interconnection with an analogintegrated circuit 31. The two devices may be coupled using conventionalinterconnect technology. In the preferred embodiment, flip chip bondingis used to connect the bonding pads (not shown) on the lower surface ofchip 31 to a corresponding series of interconnect pads 33 on thesubstrate layer 15 a. Layer 15 a is bonded to layer 15 b. Layer 15 cincludes the resilient electrical contacts. The contacts are formed bychemical etching and/or stamping. Pins 21 at each corner of layer 15 care used to assure appropriate alignment between the transceiver and thePCB or other underlying device to which it connects. In addition, in apreferred embodiment, the sides of the substrate are coated with a metallayer to reduce electromagnetic interference.

A heat spreading cap 35 provides a hermetic seal for the integratedcircuit 31 with the substrate, thereby preventing undesiredparticulates, moisture, and the like from interfering with the operationof the integrated circuit 31. Additionally the cap provides immunity toelectro-magnetic interference and prevents electromagnetic radiationfrom the transceiver. Cap 35 is preferably affixed to substrate 15 usingsolder or conductive epoxy. If desired a heat sink (not shown) can beaffixed to the heat-spreading cap 35 to dissipate heat resulting fromoperation of the integrated circuit.

FIG. 5 also illustrates the array of photodetectors 40 and the array oflaser diodes 42. Photodetectors 40 and laser diodes 42 are commerciallyavailable components, for example, if implemented as VCSELs and PINs,from Emcore Corporation. These devices electrically couple to the analogcircuit 31 through wirebonds, contact pads and substrate vias. In afurther embodiment of this invention, the light emitting devices may bedirectly coupled to the substrate lower surface contacts without beingcoupled to drivers. Similarly the light sensing devices may be directlycoupled to the substrate lower surface contacts without being coupled toTIAs.

The optical alignment of the transceiver is enabled by special featuresin the substrate. (See FIG. 6.) The optoelectronic devices are placed ina tight alignment by use of two guiding pins 25, 26 on the underside ofthe substrate 15 (see FIG. 6). The guiding pins are positioned withclose tolerance, typically on the order of a few microns. They are pressfitted or bounded to the substrate and separated by a known distance.This dimension can have a looser tolerance, e.g. 50 to 100 um, enablingless expensive packaging material and assembly technology. The first pin25 is used as geometrical reference point. Laser diodes andphoto-detectors are positioned to an accurate distance with reference tothis guiding pin 25. The combination of the two pins 25, 26 determine anaccurate orientation of the arrays of laser diodes and photodetectors.With these two guiding features the laser diodes and photo-detectors canbe very accurately oriented. Alternatively, the guiding pins can bereplaced by guiding spheres.

Similarly the multi-port lens 24 has two openings. The first round hole29 has a precise diameter and tightly fits the guiding pin 25. Thesecond hole 30 is oblong. The oblong shape is aligned with an axisformed between the first round hole 29 and the second hole 30. Theoblong hole 30 has a precise width that tightly fits the second guidingpin 26 diameter. The shape is oblong to accommodate the loose toleranceon the distance between the two guiding pins. This approach allowsprecise alignment between the lens and the substrate guiding pins, andtherefore to the laser diodes and photo-detectors.

The multiple lenses, the fibers grooves 18 and the guiding holes 29, 30are all injection-molded into the multi-ports lens 24 (see FIG. 7). Thisfabrication process ensures that all features are very precisely alignedrelative to each other. Thus by appropriate dimensioning and sizing ofthe arrays and corresponding openings in a multi-port lens 24, thephotodetectors 40 and laser diodes 42 can be appropriately alignedwithin the multi-port lens to interface with the optical fibers 10.

FIG. 7 illustrates an alternative structure for the optical transceiver.As shown there, the photodetectors 40 and laser diodes 42 are coupled totrans-impedance amplifiers (TIA) 44 and laser diode drivers 46,respectively. The connections between these devices are all electricaland accommodated by well known contact technology between the twocomponents. The drivers, TIAs and electro-optical (EO) converters residein a multilayered substrate 16 as shown. Substrate 16 is preferably ofsimilar construction and materials as described above for substrate 15.The upper surface (lower in the illustration of FIG. 7) of the substrateis coupled to a heat-spreading plate 35 a to dissipate heat from theelectronic devices. The lower surface (upper in the illustration of FIG.5) of the substrate 16 includes the array of conventional electricalconnections 50, for example of the types discussed in conjunction withFIG. 2, adapted to be connected to appropriate external modules,sockets, printed circuit boards, or the like. The multi-port lensassembly 24 is appropriately dimensioned to fit within the recessedregion of the substrate 16 a and encompass the EO converters anddrivers. As with the embodiment of FIG. 2, a series of grooves or otherappropriate alignment mechanisms molded into the lens assembly 24ensures that the optical fibers align with the lenses to provide anappropriate optical connection between the fibers and the converters. Inthe implementation depicted, the ribbon of fibers 10 is shown mounted toan underlying organic flexible layer 11 for connection to thetransceiver. As with further embodiments of FIG. 5, the light emittingdevices may be directly coupled to the substrate lower surface contactswithout being coupled to drivers. Similarly the light sensing devicesmay be directly coupled to the substrate lower surface contacts withoutbeing coupled to TIAs.

FIG. 8 is a cross-sectional view illustrating a cross section throughthe transceiver shown in FIG. 2. As illustrated in FIG. 8, grooves 18into which the optical fibers are positioned and stopping features 63 inthe multi-port lens assembly 24 cause the optical fibers 10 to alignwith light path 60 in the multi-port lens assembly 24. Note thatprotrusion 63 positions the fibers in the longitudinally-desiredlocation, while the grooves position the fibers in a perpendiculardirection. The electro-optical converters 40, 42 are shown andpositioned at essentially right angles to the longitudinal axis of thelight path 60. The collimating lenses 73 collimate the beams from thelight-emitting elements, preferably VCSELs 42, and a total internalreflection interface 66 turns the beams. Then focusing lenses 75 focusthe beams into the optical fibers 10. On the photodetector side, thecollimating lenses 76 collimate the multimode fiber beams and a totalinternal reflection interface 66 reflects the beams. The beams arefocused through focusing lenses 74 onto the photodetectors. Solder bumps68 couple the substrate 15 to the integrated circuit 31. As mentionedabove, vias (not shown) through the intervening layers in substrate 15enable the electro-optical converters to be electrically connected tothe integrated circuit 31.

FIG. 9 illustrates in cross section the embodiment of the opticaltransceiver shown in FIG. 7. The diagram of FIG. 9 is similar to that ofFIG. 8. Note, however, that the driver or analog circuit 31 is mountedinto the substrate recess under the lens assembly 24 enabling a thinner,more compact package. Additionally the TIA and driver circuits are wirebonded 64 to the substrate and the electro-optical converters.

FIG. 10 is a perspective view illustrating in more detail the lensassembly 24, the manner in which the optical fibers 10 interface withthe lens assembly 24, the internal reflection surface 66, and thestaggered arrangement of the electro-optical converters 40 and 42. Thecompliant contacts are also shown. The staggered arrangement enables aregular pitch all along the fiber ribbon (250 um pitch). If placedimmediately adjacent to each other the VCSELs array and PINs array wouldnot allow this periodic pitch, or would require (wasted) dark fibersbetween the receiving fibers and the transmitting fibers

FIGS. 11-13 illustrate typical applications for a transceiver 12according to the embodiments described above. As shown in FIG. 11, thetransceiver 12 is mounted on an optical host card adapter 150 for beingcoupled to a PCI express bus. The illustration shows a server board 100having two CPUs 110, a memory controller hub 120, a series of memorycards 130, and a PCI express bus riser 140. An optical host card adapter150 plugs into the bus riser 140 to enable optical connections betweenthe server board and its affiliated hardware with the desired externalsystems via the optical transceiver 12. As mentioned earlier, the use ofthe optical transceiver and host card 150 are particularly suitable forinput/output intensive applications, graphic processing, and other highbandwidth server applications.

FIG. 12 illustrates a similar server motherboard to that depicted inFIG. 11. In FIG. 12, however, the optical transceiver 12 is integratedonto the motherboard 100, eliminating the need for the riser card 140and the optical host card 150.

FIG. 13 illustrates another implementation of the optical transceiver.In this case the transceiver is employed in one slot of the memory cardbus and used to provide a high speed connection to additional memory. Inthe implementation shown in FIG. 13, additional memory can be added tothe server without need of replacement of the server motherboard 100.

As described above, the optical transceiver of this invention provides atransceiver in which a multilayer substrate is used as a base component.Each of the other components—the photodetectors, laser diodes,integrated circuit, lens, and heat spreader, are all attached to thesubstrate. The substrate itself provides a structural role as theskeleton of the transceiver, eliminating need for a special enclosure.Thus, in contrast to other conventional optical transceiver designs,this transceiver does not require a special enclosure. As alsodescribed, the transceiver is easily electrically coupled to a printedcircuit board, a grid array socket, or other conventional electronicinterfaces. The resulting structure provides electrical connections,heat conduction, and electromagnetic radiation barriers as needed. Thetransceiver provides for a smaller form factor than convention opticaltransceivers. The photodetectors and laser diodes can be provided on thesame substrate in nearby locations, in contrast to the need for use ofseparate modules as in some prior art solutions.

Although various embodiments and implementation details of the opticaltransceiver of this invention have been described above in a preferredembodiment, it will be appreciated that the scope of the invention isdetermined by the appended claims.

1. An electro-optical transmitter comprising: a substrate having agenerally planar configuration including an upper surface, a lowersurface and an edge between the upper and the lower surfaces, and havinga recess therein with a bottom surface with at least one openingtherein; a multi-port lens affixed to the bottom surface of the recess;an integrated circuit affixed to the bottom surface of the recess, aplurality of light emitting devices mounted to communicate opticallywith the multi-port lens, each of the plurality of light emittingdevices being electrically coupled to the at least one integratedcircuit; a set of electrical contacts disposed on the lower surface ofthe substrate for connection to external circuitry, the set ofelectrical contacts being coupled through the substrate to the at leastone integrated circuit; a plurality of optical fibers coupled throughthe edge of the substrate to the multi-port lens, individual ones of theoptical fibers being positioned to communicate optically with individualones of the light emitting devices; wherein electrical signals from theintegrated circuit are converted to optical signals for transmission onthe optical fibers, and wherein the electrical signals are provided tothe lower surface of the substrate, heat is dissipated from the uppersurface of the substrate, and optical signals are transmitted along theedge of the substrate.
 2. A transmitter as in claim 1 wherein themulti-port lens includes lens apparatus for directing light from thelight emitting devices into the optical fibers.
 3. A transmitter as inclaim 2 wherein: the plurality of light emitting devices is affixed tothe substrate to emit light in a direction perpendicular to the lowersurface; and the multi-port lens includes a pathway for light from thelight emitting devices to be transmitted into the optical fiber.
 4. Atransmitter as in claim 3 wherein the lens assembly further includes aseries of grooves and a series of stops for positioning the opticalfibers in alignment with the light emitting devices.
 5. A transmitter asin claim 1 wherein the set of electrical contacts comprise electricallyconductive regions on the lower surface of the substrate for connectionto external circuitry, the external circuitry including a carrier withcompliant bumps containing metal particles to be pressed againstcorresponding ones of the electrically conductive regions on the lowersurface of the substrate.
 6. A transmitter as in claim 1 wherein thefirst set of electrical contacts comprises a series of compliant fingerportions positioned over recessed areas in the substrate to enable themto be pressed against contact regions coupled to the external circuitry.7. A transmitter as in claim 1 wherein the set of electrical contactscomprise electrically conductive regions on the lower surface of thesubstrate for connection to external circuitry, the external circuitryincluding a carrier having compliant fingers to secure the substrate tothe carrier and wherein the carrier includes compliant pins adapted tobe pressed against corresponding ones of the electrically conductiveregions on the lower surface of the substrate.
 8. A transmitter as inclaim 1 wherein the plurality of light emitting devices comprisevertical cavity surface emitting laser diodes.
 9. A transmitter as inclaim 1 further comprising a heat spreader over the integrated circuitto improve heat spreading from the integrated circuit and to reduceelectromagnetic radiation.
 10. A transmitter as in claim 2 wherein oneof the multi-port lens and the substrate include at least two guidefeatures, and the other includes at two corresponding openings, toenable alignment of the multi-port lens and the substrate with eachother.
 11. A transmitter as in claim 10 wherein the correspondingopenings comprise a cylindrical opening and an elongated opening.
 12. Atransmitter as in claim 1 wherein the light emitting devices are alignedto the substrate with guide features in the substrate.
 13. A transmitteras in claim 1 wherein the substrate includes a metallic coating disposedaround the edge to reduce electromagnetic radiation.
 14. A transmitteras in claim 2 wherein the substrate does not include a recessed regionand wherein the multi-port lens and the integrated circuit are mounteddirectly on the lower surface of the substrate.
 15. An electro-opticaltransmitter comprising: a substrate having a generally planarconfiguration including an upper surface, a lower surface and an edgebetween the upper and the lower surfaces, and having a recess thereinwith a bottom surface with at least one opening therein; a first set ofelectrical contacts for connection to external circuitry, the first setof electrical contacts being disposed on the lower surface of thesubstrate; a second set of electrical contacts disposed on the uppersurface of the substrate, the second set of contacts being electricallyconnected through the substrate to the first set of contacts; anintegrated circuit affixed to the upper surface of the substrate andelectrically connected to the second set of contacts; a multi-port lensaffixed to the bottom surface of the recess; a plurality of lightemitting devices mounted to communicate optically with the multi-portlens, each of the plurality of light emitting devices being electricallycoupled through the substrate to the integrated circuit; and a pluralityof optical fibers coupled through the edge of the substrate to themulti-port lens, individual ones of the optical fibers being positionedto communicate optically with individual ones of the light emittingdevices; wherein electrical signals from the integrated circuit areconverted to optical signals for transmission on the optical fibers, andwherein the electrical signals are provided to the lower surface of thesubstrate, heat is dissipated from the upper surface of the substrate,and optical signals are transmitted along the edge of the substrate. 16.A transmitter as in claim 15 wherein the multi-port lens includes lensapparatus for directing light from the light emitting devices into theoptical fibers.
 17. A transmitter as in claim 16 wherein: the pluralityof light emitting devices is affixed to the substrate to emit light in adirection perpendicular to the lower surface; and the multi-port lensincludes a pathway for light from the light emitting devices to betransmitted into the optical fiber.
 18. A transmitter as in claim 17wherein the lens assembly further includes a series of grooves and aseries of stops for positioning the optical fibers in alignment with thelight emitting devices.
 19. A transmitter as in claim 15 wherein the setof electrical contacts comprise electrically conductive regions on thelower surface of the substrate for connection to external circuitry, theexternal circuitry including a carrier with compliant bumps containingmetal particles to be pressed against corresponding ones of theelectrically conductive regions on the lower surface of the substrate.20. A transmitter as in claim 15 wherein the first set of electricalcontacts comprises a series of compliant finger portions positioned overrecessed areas in the substrate to enable them to be pressed againstcontact regions coupled to the external circuitry.
 21. A transmitter asin claim 15 wherein the first set of electrical contacts compriseelectrically conductive regions on the lower surface of the substratefor connection to external circuitry, the external circuitry including acarrier having complaint fingers to secure the substrate to the carrierand wherein the carrier includes compliant pins adapted to be pressedagainst corresponding ones of the electrically conductive regions on thelower surface of the substrate.
 22. A transmitter as in claim 15 whereinthe plurality of light emitting devices comprise vertical cavity surfaceemitting laser diodes.
 23. A transmitter as in claim 15 furthercomprising a metallic cap over the integrated circuit to improve heatspreading from the integrated circuit and to reduce electromagneticradiation.
 24. A transmitter as in claim 16 wherein one of themulti-port lens and the substrate include at least two guide features,and the other includes at two corresponding openings, to enablealignment of the multi-port lens and the substrate with each other. 25.A transmitter as in claim 24 wherein the corresponding openings comprisea cylindrical opening and an elongated opening with the elongateddirection in the axis formed by the two openings.
 26. A transmitter asin claim 24 wherein the light emitting devices are aligned to thesubstrate with guide features in the substrate.
 27. A transmitter as inclaim 15 wherein the substrate includes a metallic coating disposedaround the edge to reduce electromagnetic radiation.
 28. A transmitteras in claim 16 wherein the substrate does not include a recessed regionand wherein the multi-port lens and the integrated circuit are mounteddirectly on the lower surface of the substrate.